Optical beam scanning device and diaphragm device

ABSTRACT

An optical beam scanning device of the present invention has a light source, a deflection reflecting surface for deflecting to scan light from the light source on a recording medium, and a diaphragm device which is provided between the light source and the deflection reflecting surface, and the diaphragm has an opening section formed by a nonplanar light shielding section. The light shielding section makes light shielding quantity of the light from the light source in a vertical scanning direction different in positions in a horizontal scanning direction and in a light advancing direction.

BACKGROUND OF THE INVENTION

The invention relates to an optical beam scanning device and a diaphragmdevice. For example, the invention relates to the optical beam scanningdevice which is capable of adjusting light quantity distribution oflaser beams reaching a scanning surface, and the diaphragm device foruniforming light quantity distribution of a light flux section ofemitted light vertical to a light advancing direction.

Conventionally, optical scanning devices adopt roughly two kinds ofsystems for scanning light from light sources on recording media.

One of them is a system for allowing laser beams narrower than an imagewidth of a reflecting surface of a rotating polygon mirror enter in ahorizontal scanning direction and scanning them (hereinafter, “underfield type”). The other one is a system for allowing laser beams widerthan the image width of the reflecting surface of the rotating polygonmirror in the horizontal scanning direction enter and scanning a part ofthe laser beams cut off by the reflecting surface (hereinafter, “overfield type”).

In order to solve non-uniformity of light quantity distribution onrecording media in the over field type optical beam scanning devices,conventionally, the following technique for correcting light quantitydistribution on recording media is present.

Japanese Unexamined Patent Application Publication No. 11-218702discloses that in the over field type optical beam scanning device, anaperture plate is provided between a collimating lens and a concave lensand an opening shape of the aperture plate is such that a length in avertical scanning direction on both end positions in a horizontalscanning direction is larger than a length on a center position in thehorizontal scanning direction.

Japanese Unexamined Patent Application Publication No. 2001-108926discloses that in an over field type optical beam. scanning system, aslit member having a slit is provided on a halfway optical path betweena light source and a polygon mirror and a slit shape is determined sothat a light quantity for exposing positions on a surface to be scanned(on a recording medium) from a scanning start position to a scanning endposition in one scanning becomes approximately constant.

Japanese Unexamined Patent Application Publication No. 2001-125033discloses that in an over field optical beam scanning system, adiaphragm, in which an aperture diameter in a vertical scanningdirection on at least one peripheral portion of a condensing lens systemis wider than that at a center of the condensing lens system, isprovided between a laser light source and a polygon mirror.

Japanese Unexamined Patent Application Publication No. 2002-023092discloses that in order to uniform light quantity distribution on arecording medium in an over field type optical beam scanning device, apositional relationship between a rotating polygon mirror and a laserbeam is set as follows. When an effective reflecting width of areflecting surface of the rotating polygon mirror becomes small, a partof a laser beam with large light intensity distribution is reflected,and when the effective reflecting width of the reflecting surfacebecomes large, a part of the laser beam with small light intensitydistribution is reflected.

In an actual laser beam, however, light intensity in Gaussiandistribution disperses to a certain degree. In Japanese UnexaminedPatent Application Publication Nos. 11-218702(1999), 2001-108926 and2001-125033, however, since a correcting amount of the light quantitydistribution is fixed, these techniques cannot cope with dispersion of alaser beam.

In Japanese Unexamined Patent Application Publication No. 2002-023092,the light quantity distribution can be corrected in a device in which achange in the effective reflecting surface always increases or decreases(so-called over field type optical beam scanning device for grazingincidence). The light quantity distribution can be,however, corrected inonly one of the cases where the change in the effective reflectingsurface increases and decreases (so-called over field type optical beamscanning device for front incidence). Further, in Japanese UnexaminedPatent Application Publication No. 2002-023092, a light quantity on arecording medium is reduced further towards a right end of a graph inthe embodiment, and thus the light quantity is not completely corrected.

Further, in Japanese Unexamined Patent Application Publication No.2002-023092, a displacement unit which enables an incident position of alaser beam to be displaced in a light scanning direction is provided sothat adjustment is possible. Since a total number of parts increases anda light source is moved, however, locating of an optical axis becomes aproblem.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide an inexpensivediaphragm device with reliability which adjusts a light quantity ofincident light and corrects light quantity distribution of emitted lightso as to adjust its correcting amount, and an optical beam scanningdevice which is capable of correcting light quantity distribution on arecording medium considering after dispersion of light intensity inGaussian distribution of light source light and an effective reflectingwidth of a reflecting surface of a rotating polygon mirror.

An optical beam scanning device from a first aspect of the invention ischaracterized by including: a light source; a deflection reflectingsurface for deflecting to scan light from the light source on arecording medium; and a diaphragm device provided between the lightsource and the deflection reflecting surface, the diaphragm devicehaving an opening section formed by a nonplanar light shielding section,the light shielding section making a light shielding quantity of thelight from the light source in a vertical scanning direction differentin positions of a light advancing direction.

An optical beam scanning device from a second aspect of the invention ischaracterized by including: a cylindrical lens for condensing light froma light source; a deflection reflecting surface for deflecting to scanthe light from the light source on a recording medium; an aperture plateprovided between the cylindrical lens and the deflection reflectingsurface, its opening section on a surface having a shape such that alength in a direction crossing a horizontal scanning direction on bothends or one end in a scanning direction is larger than a length on acenter portion in the scanning direction; and a movable adjustmentsection for shifting an installation position of the aperture plateand/or giving certain curvature to the aperture plate and thus asectional shape in the horizontal scanning direction is a curved lineshape so as to adjust light quantity distribution on the recordingmedium uniformly.

An optical beam scanning device from a third aspect of the invention ischaracterized by including: a light source; a deflection reflectingsurface for deflecting to scan light from the light source on arecording medium; an aperture plate provided between the light sourceand the deflection reflecting surface, its opening section on a surfacehaving a shape such that a length in a direction crossing a horizontalscanning direction on both ends or one end in a scanning direction islarger than a width on a center portion in the scanning direction, itssectional shape in the horizontal scanning direction being atwo-dimensional shape; and a movable adjustment section for moving aninstallation position of the aperture plate and/or giving certaincurvature to the aperture plate so that the sectional shape in thehorizontal scanning direction is a curved line shape so as to adjustlight quantity distribution on the recording medium uniformly.

A diaphragm device from a fourth aspect of the invention ischaracterized by including: an opening section on a surface of anonplanar light shielding section, wherein the light shielding sectionshields light so that a position where incident light ofconverged/diverged light or parallel light is shielded is differed witha light advancing direction according to positions in a light section.

A diaphragm device from a fifth aspect of the invention is characterizedby including: an opening section on a surface of a nonplanar lightshielding section, wherein the light shielding section determines aquantity of incident light of converged/diverged light or parallel lightto be shielded according to positions in a light section and positionsof a light advancing direction.

According to the diaphragm device of the present invention, the lightquantity of emitted light can be corrected and the correcting amount ofthe light quantity distribution of the emitted light can be adjustedwith a simple and inexpensive constitution.

Further, according to the optical beam scanning device of the presentinvention, the correcting amount of the light quantity distribution on arecording medium can be adjusted by using the simple and inexpensivediaphragm device.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a constitutional diagram illustrating a constitution of anoptical beam scanning device according to a first embodiment;

FIGS. 2A to 2C are explanatory diagrams explaining an example of anaperture shape and a state of a passing laser beam in the case of frontincidence according to the first embodiment;

FIGS. 3A to 3C are explanatory diagrams explaining an example of theaperture shape and a state of the passing laser beam in the case ofgrazing incidence according to the first embodiment;

FIGS. 4A and 4B are diagrams illustrating a shape of a passing laserbeam from a aperture with a curved-line shape in the case of the frontincidence according to the first embodiment;

FIG. 5A and 5B are diagrams illustrating a shape of a passing laser beamfrom the aperture with a curved-line shape in the case of the grazingincidence according to the first embodiment;

FIGS. 6A to 6C are diagrams illustrating a modified example of theaperture shape in the case of the front incidence according to the firstembodiment;

FIGS. 7A to 7C are diagrams illustrating a modified example of theaperture shape in the case of the grazing incidence according to thefirst embodiment;

FIGS. 8A and 8B are diagrams illustrating a shape of a laser beamemitted from a binary-shaped aperture in the case of the front incidenceaccording to the first embodiment;

FIGS. 9A and 9B are diagrams illustrating a shape of a laser beamemitted from the binary-shaped aperture in the case of the grazingincidence according to the first embodiment;

FIGS. 10A to 10D are explanatory diagrams explaining modified examplesof the aperture shape according to the first embodiment;

FIGS. 11A and 11B are explanatory diagrams explaining a modifyingoperation of the curved-line aperture according to the first embodiment;

FIG. 12 is a constitutional diagram illustrating a constitution of theoptical beam scanning device according to a second embodiment;

FIGS. 13A to 13C are explanatory diagrams explaining an example of theaperture shape and a state of the passing laser beam in the case of thefront incidence according to the second embodiment;

FIGS. 14A to 14C are explanatory diagrams explaining an example of theaperture shape and a state of the passing laser beam in the case of thegrazing incidence according to the second embodiment; and

FIGS. 15A and 15B are explanatory diagrams illustrating a difference oflight quantity adjustment due to a difference in the aperture shapeaccording to a third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

An optical beam scanning device and a diaphragm device according topreferred embodiments of the present invention are explained below withreference to the drawings.

The following embodiments explain the case where the diaphragm device ofthe present invention is applied to an over field type optical beamscanning device. The diaphragm device of the present invention is notlimited to this, and can be applied also to light quantity adjustmentof, for example, an image scanner, a printer, a facsimile, an MFP and acamera.

(A) Constitution of First Embodiment

The optical beam scanning device and the diaphragm device according to afirst embodiment of the present invention are explained below withreference to FIGS. 1 to 11.

In the first embodiment, the diaphragm device of the present inventionis applied to the over field type optical beam scanning device, and thediaphragm device is provided between a cylindrical lens and a rotatingpolygon mirror. The diaphragm device adjusts a light quantity of emittedlight so that light quantity distribution on a recording medium isfinally uniformed.

FIG. 1 is a constitutional diagram illustrating a constitution of anoptical beam scanning device of this embodiment. As shown in FIG. 1, theoptical beam scanning device of the embodiment has an aperture (openingmember) 1, a laser light source 2, a collimating lens 3, a cylindricallens 4, and a rotating polygon mirror 5.

The aperture 1 of the embodiment corresponds to the diaphragm device ofthe present invention.

The laser light source 2 is composed of, for example, a semiconductorlaser or the like, and is an emitting unit for emitting a laser beam.

The collimating lens 3 converts a laser beam as diverged light emittedfrom the laser light source 2 into parallel light.

The cylindrical lens 4 condenses the laser beam from the collimatinglens 3 to a vertical scanning direction.

The rotating polygon mirror 5 reflects a laser beam whose light quantityis adjusted by the aperture 1, by a reflecting surface so as to emit thelaser beam to a recording medium, not shown.

The aperture 1 has an opening section at the center of one plate such aselastic sheet metal so as to be formed into a two-dimensional shapehaving curvature in a light advancing direction. In the embodiment, theopening section of the aperture 1 has a rectangular shape, but the shapeof the opening section is not particularly limited.

Hereinafter, the opening section of the aperture 1 means an openingsection on a surface extended portion of the shape of the aperture 1.Even when the aperture 1 has a two-dimensional shape, the openingsection is an opening on the surface of the shape of the aperture 1. Theopening section of the aperture 1 includes an optical opening to whichtransmitting glass, resin or the like is attached.

The aperture 1 is provided between the cylindrical lens 4 and therotating polygon mirror 5, and allows light positioned on the openingsection in a light flux (vertical section in the light advancingdirection) of the light (converged light) from the cylindrical lens 4 topass therethrough. The aperture 1 shields light positioned in portionsother than the opening section (the shielding portion of the aperture 1is called as a light shielding section). In the embodiment, the aperture1 is provided between the cylindrical lens 4 and the rotating polygonmirror 5, but its installation position is not limited as long as it isbetween the light source 1 and the rotating polygon mirror 5. Theaperture may be provided between, for example, the light source 2 andthe collimating lens 3 so as to be applied to diverged light. Further,the aperture 1 may be provided between, for example, the collimatinglens 3 and the cylindrical lens so as to be applied to parallel light.

The aperture 1 has, as mentioned above, the two-dimensional shape in thelight advancing direction. For this reason, the light from thecylindrical lens 3 is shielded at different timings according topositions in a horizontal scanning direction of a light flux sectionvertical to the light advancing direction.

That is to say, when the opening section of the aperture 1 has therectangular shape in which its height in the vertical scanning directionis uniform on entire area in the horizontal scanning direction like theembodiment, as the timing at which the light is shielded by the aperture1 (light shielding timing) get later, a condensing distance of the laserbeam passing through the opening section of the aperture 1 can be longerand a degree of the light shielding in the vertical scanning directioncan be decreased. For this reason, the light shielding timing getslater, the light quantity of the light passing through the openingsection in the vertical scanning direction can be increased.

According to this, the aperture 1 has such a two-dimensional shape thatthe light shielding timing gets later on a portion where the lightintensity of a laser beam in the Gaussian distribution is weak than thaton a portion where the light intensity is strong. A sectional shape of alight flux passing through the opening section of the two-dimensionalaperture 1 (a projected shape of the passing light on a certain virtualsurface after passing) is determined so that a length in the verticalscanning direction becomes larger in a position where the lightshielding timing is comparatively late or a length in the verticalscanning direction becomes small in a position where the light shieldingtiming is comparatively early. As a result,the light quantity can becorrected so that the light quantity distribution on a recording mediumbecomes uniform.

Similarly, the aperture 1 has a such a shape that the light shieldingtiming gets later on a portion where an effective reflecting width ofthe reflecting surface of the rotating polygon mirror 5 is narrower thanon a portion where the effective reflecting width of the reflectingsurface of the rotating polygon mirror 5 is wide.

FIGS. 2A to 2C are diagrams explaining an example of a curved line shapeof the aperture 1 and a state of a passing laser beam from the aperture1 to the rotating polygon mirror 5 in the case of front incidence. FIGS.3A to 3C are diagrams explaining an example of the curved line shape ofthe aperture 1 and a state of the passing laser beam from the aperture 1to the rotating polygon mirror 5 in the case of grazing incidence.

FIG. 2A is a top view in which advance of the light beam is viewed froma top of the optical beam scanning device, FIG. 2B is a side view inwhich the advance of the light beam is viewed from a side of the opticalbeam scanning device, and FIG. 2C is a sectional view in which a sectiontaken along line A-A of FIG. 2B is viewed from a side of the rotatingpolygon mirror 5.

As shown in FIG. 2A, in the case of the front incidence, the sectionalshape of the aperture 1 in the horizontal scanning direction(hereinafter, the shape of the aperture 1) is a curved line shape havinguniform curvature on both ends.

This shape is determined after the following is taken intoconsideration. In the case of the front incidence, the reflectingsurface of the rotating polygon mirror 5 reflects light to a recordingmedium symmetrically with respect to an optical axis of incident light.The effective reflecting width of the reflecting surface due to rotationof the rotating polygon mirror 5 and the light intensity of the incidentlight entering the reflecting surface in the Gaussian distributionbecome maximum when an oscillation angle of the reflecting surface onthe optical axis of the incident light becomes 0°. The effectivedeflecting width and the light intensity become smaller as thereflecting surface and the optical axis of the incident light form theoscillation angle.

In order to uniform the light quantity on a recording medium, therefore,the aperture 1 has the curved line shape having uniform curvature onboth ends. As a result, the sectional shape of the light flux passingthrough the opening section is such that a height of both the ends inthe vertical scanning direction is larger than a height of the centerportion in the vertical scanning direction.

FIGS. 3A to 3C correspond to FIGS. 2A to 2C.

In FIG. 3A, the aperture 1 in the case of the grazing incidence has thecurve line shape having large curvature in a direction where thereflecting effective width of the rotating polygon mirror 5 decreases.Needless to say, the shape of the aperture 1 is not limited to this, andfor example, the aperture 1 may be formed considering the lightintensity in Gaussian distribution of a laser beam reflected by thereflecting surface of the rotating polygon mirror.

Similarly to the case of the front incidence, the effective reflectingwidth of the reflecting surface due to the rotation of the rotatingpolygon mirror 5 and the light intensity in the Gaussian distribution ofthe incident light entering the reflecting surface are taken intoconsideration.

The sectional shape of the light flux passing through the openingsection of the aperture 1 shown in FIGS. 2A to 3C is explained withreference to FIGS. 4A to 5B. FIGS. 4A and 4B illustrate the case of thefront incidence, and FIGS. 5A and 5B illustrate the case of the grazingincidence.

As shown in FIGS. 4A and 4B or 5A and 5B, curvature is given to theshape of the aperture 1 so that the light shielding timing is adjusted.As a result,the sectional shape of the light flux passing through theaperture 1 is such that the length of both the ends or one end in thevertical scanning direction is larger than the length of the centerportion in the vertical scanning direction. The light quantity on aportion where the light intensity in the light quantity distribution isweak can be corrected.

Modified examples of the shape of the aperture 1 are explained belowwith reference to FIGS. 6A to 9B.

FIGS. 6A to 6C illustrate modified examples of the shape of the aperture1 in the case of the front incidence, and FIGS. 7A to 7C illustratemodified examples of the shape of the aperture 1 in the case of thegrazing incidence.

FIGS. 6A and 7A illustrate the above-mentioned curved line shape, andFIGS. 6B, 6C, 7B and 7C illustrate modified examples of the shape of theaperture 1.

In the modified examples shown in FIGS. 6B and 7B, the shapes aredetermined considering an installation space in the optical beamscanning device, and the sectional shape in the horizontal scanningdirection is composed of a plurality of binary shapes (stepped shape).

When the curved line shape of FIGS. 6A and 7A is provided, one flatplate is provided with curvature so as to have the curved line shape.For this reason, the installation space of the aperture 1 becomes large.

In order to solve this problem, the aperture 1 has the binary shapeshown in FIGS. 6B and 7B, so that the installation space can be smallerthan the case of the curved line shape.

In the case where the aperture 1 has the curved line shape, locating(fulcrum) places should be increased in order to create a complicatedcurvature shape which can completely correct the light quantitydistribution of a laser beam. In the case of the binary shape, however,for example, the aperture 1 is manufactured by press work or the like sothat a stable shape can be easily created.

In the case where the aperture 1 has the binary shape, the sectionalshape of the light flux passing through the opening section of theaperture 1 is as shown in FIGS. 8A to 9B.

FIGS. 8A and 8B illustrate the sectional shape of the light flux passingthrough the opening section of the aperture 1 in the case of the frontincidence, and FIGS. 9A and 9B illustrate the sectional shape in thecase of the grazing incidence.

As shown in FIGS. 8A and 8B, the sectional shape of the light flux inthe case of the binary shape is approximate to the sectional shape ofthe light flux in the case of the curved line shape in FIG. 4B, and canobtain a performance which is close to that of the curved line shape.When a number of steps in the binary shape is increased, the performancewhich is closer to that of the curvedline shape can be obtained. In thecase of the binary shape, corners of the steps may be inscribed in orcircumscribed about the above-mentioned curved line, or a midpoint of aside of the step in the horizontal scanning direction may pass throughthe curved line.

Also in the case of FIGS. 9A and 9B, the sectional shape of the lightflux in the case of the binary shape is approximate to the sectionalshape of the light flux in the case of the curved line shape in FIG. 5B,so that the performance close to that of the curved line shape can beobtained.

With reference to FIGS. 6A to 7C, the modified examples of the aperture1 shown in FIGS. 6C and 7C are explained.

In FIGS. 6C and 7C, the polygonal shapes are inscribed in orcircumscribed about the curved line with respect to the light advancingdirection, or midpoints of the sides pass through the curved line sothat the polygonal shapes are approximate to the curved line shapes inFIGS. 6A and 7A.

The polygonal shapes in FIGS. 6C and 7C can reduce the installationspace similarly to the binary shape, and can provide the performanceclose to that of the curved line shape. In this case, as a number ofcorners to be set increases further, the performance which is closer tothat of the curved line shape can be obtained.

The case where the above-mentioned aperture 1 adjusts the correctingamount of the light quantity distribution on a recording medium isexplained below with reference to FIGS. 10A to 11B.

According to the adjusting method for the correcting amount of the lightquantity distribution on a recording medium in the embodiment, the shapeof the above-mentioned aperture 1 is modified and the installationposition of the aperture 1 is moved, so that the light quantitydistribution on the recording medium is corrected.

FIGS. 10A to 10D illustrate examples where the shape of the aperture 1is modified. FIG. 10A illustrates the example where the curved lineshape of the front incidence is modified, and FIG. 10B illustrates theexample where the binary shape of the front incidence is modified. FIG.10C illustrates the example where the curved line shape of the grazingincidence is modified, and FIG. 10D illustrates the example where thebinary shape of the grazing incidence is modified.

As shown in FIGS. 10A to 10D, a moment to the vertical scanningdirection is given to both the ends or one end of the aperture 1 by, forexample, deforming adjustment units 20 shown in FIG. 11 foroptimization. As a result, the shape of the aperture 1 is changed, andthe correcting amount in the light quantity distribution of the laserbeam passing through the aperture 1 in the horizontal scanning directioncan be adjusted.

FIGS. 10A to 10D illustrate the case where the moment to the verticalscanning direction is given so that the aperture 1 is deformed. A loadmay be, however, applied to the aperture 1 from any direction as long asthe aperture 1 is deformed and thus a phase of the light shielding canbe changed. For example, a load of the light advancing direction or itsopposite direction is applied to any one of the upper end or the lowerend of the aperture 1 in the vertical scanning direction so that theaperture 1 may be bent in the vertical scanning direction.

The deforming adjustment units 20 for deforming the shape of theaperture 1 shown in FIGS. 11A and 11B may, for example, adjust themoment to be given to the aperture 1 based on a light quantity measuredresult obtained by a sensor provided in the vicinity of the recordingmedium. For example, in the case of the front incidence shown in FIG.11A, scanning angles with respect to the optical axis of the incidentlight are symmetrical in the horizontal scanning direction. For thisreason, a fixed point 21 (for example, a protrusion) for fixing theaperture 1 is provided in a position where the light flux of theincident light is not disturbed and the deforming adjustment units 20 onboth the ends cooperate so as to modify the aperture.

In the case where the installation position of the curved line-shapedaperture 1 for the front incidence is adjusted, the installationposition of the aperture 1 can be moved parallel with the optical axisor to a direction vertical to the optical axis. When the installationposition of the aperture 1 is moved, a diameter of the passing laserbeam changes, but an absolute quantity of the light quantity in theentire scanning area can be adjusted. Further, any one end of theaperture 1 is moved to the horizontal scanning direction, balance of theright and left light quantity of the emitted laser beam can be adjusted.

The installation position of the aperture 1 may be shifted by thedeforming adjustment units 20 shown in FIGS. 11A and 11B. The deformingadjustment units 20 in this case may, for example, adjust theinstallation position of the aperture 1 so that the installationposition shift back and forth in the light advancing direction or itsopposite direction based on the light quantity measured result obtainedby the sensor in the vicinity of the recording medium. In the case ofthe front incidence of FIG. 11A, the fixed point 21 is cooperated withthe deforming adjustment units 20 on both the ends so that theinstallation position of the aperture 1 can be shifted without changingthe curvature of the aperture 1.

According to the first embodiment, the aperture 1 having thetwo-dimensional sectional shape in the horizontal scanning direction isprovided between the cylindrical lens 4 and the rotating polygon mirror5. As a result, the light quantity of the light from the cylindricallens 4 can be adjusted so that the light quantity distribution on arecording medium becomes uniform.

Further, the sectional shape of the aperture 1 in the horizontalscanning direction is deformed, and/or the installation position of theaperture 1 is shifted, so that the correcting amount of the lightquantity distribution can be adjusted.

(B) Constitution of Second Embodiment

The case where optical beam scanning device and the diaphragm deviceaccording to a second embodiment of the present invention are applied toan over field type optical beam scanning device is explained below withreference to FIGS. 12 to 14C.

FIG. 12 is a diagram illustrating a constitution of the optical beamscanning device according to the second embodiment.

The second embodiment has the laser light source 2 as a light source,the collimating lens 3 for converting diverged light from the laserlight source 2 into parallel light, the cylindrical lens 4 forconverging the laser beams to the vertical scanning direction, therotating polygon mirror 5, and the aperture (opening member) composed ofa pair of plates 7 and 8.

In the constitution of the second embodiment shown in FIG. 12, parts ofthe constitution corresponding to those of the constitution in the firstembodiment shown in FIG. 1 are designated by corresponding numbers, andthe explanation of their functions is omitted.

In this embodiment, the aperture composed of the two plates correspondsto that in the diaphragm device of the present invention.

The plates 7 and 8 composing the aperture are paired vertically in thelight advancing direction and have a predetermined angle. The plates 7and 8 are provided between the collimating lens 3 and the cylindricallens 4 and are combined so as to form an opening section.

The plates 7 and 8 are provided so as to have a certain angle to thehorizontal scanning direction, and thus have a light shielding functionfor shielding incident light and a light quantity correcting function.The angles to be set on the plates 7 and 8 can be set independently,and, for example, the angles can be set to the same value or differentvalues. In this embodiment, the plates 7 and 8 are installed inpositions where the angles are symmetrical with respect to the opticalpath.

In this embodiment, the installation position of the paired plates 7 and8 is between the collimating lens 3 and the cylindrical lens 4, but theymay be installed in any position as long as the position is between thelaser light source 2 and the rotating polygon mirror 5.

In FIG. 12, 9 designates a virtual plane in which the light advancingdirection is a normal line, and 10 designates a sectional shape of thelaser beam projected on the virtual plane 9. The shape 10 projected onthe virtual plane 9 is determined according to the shape of the plates 7and 8, the installation positional relationship between the plates, andtilt angles of the plates to the horizontal scanning direction.

The shape of the opening section formed by the plates 7 and 8 isexplained below.

FIGS. 13A to 13C are diagrams explaining a shape example of the openingsection formed by the plates 7 and 8 and a state of the laser beampassing through the opening section formed by the plates 7 and 8 in thecase of the front incidence. FIGS. 14A to 14C are diagrams illustratinga shape example and a state of the laser beam in the case of the grazingincidence.

The plates 7 and 8 shown in FIG. 13A are positioned symmetrically withrespect to the optical axis, and have a curve line shape havingcurvature such that both ends are deflected uniformly. In order toprovide the light shielding function and the light quantity distributioncorrecting function, the upper plate 7 has a constant angle to acounterclockwise (or clockwise) direction in the horizontal scanningdirection, and the lower plate 8 has a constant angle to a clockwise (orcounterclockwise) direction in the horizontal scanning direction.

The plates 7 and 8 in the case of the grazing incidence shown in FIG.14A are positioned symmetrically with respect to the optical axissimilarly to the case of the front incidence. The plates. 7 and 8 in thecase of the grazing incidence have a shape having large curvature in adirection where the effective reflecting width of the reflecting surfaceof the rotating polygon mirror 5 decreases.

As not shown, but the plates 7 and 8 may have the binary shape (steppedshape) or the polygonal shape, mentioned above, so that theirinstallation space is decreased and a complicated curvature shape may beeasily created.

Their modified examples are explained below. The two-dimensional shapeof the-plates, the installation positional relationship between theplates, tilts of the plates, and the like are changed. As a result, theopening shape 10 projected on the plane 9 where the light beam advancingdirection is the normal line is changed, and thus the correcting amountof the light quantity distribution may be adjusted.

For example, the installation position of the plates 7 and 8 is moved tothe horizontal scanning direction or the plates 7 and 8 are rotated inthe horizontal scanning direction so that the tilts of the plates 7 and8 with respect to the light advancing direction are changed. A moment tothe vertical scanning direction is given to both the ends or one end ofthe plates, so that the plates 7 and 8 may be deformed. For example, theplates 7 and 8 may be rotated about the optical axis of the laser beam.

The deformation or the like of the plates may be adjusted by thedeforming adjustment unit or the like explained in the first embodimentbased on the measured result of the light quantity distribution on arecording medium.

The plates 7 and 8 are formed by an elastic material such as sheetmetal, so that the sectional shape can be deformed easily. A moment isgiven to both the ends or one end of the plates and deflects the plates,so that the correcting amount of the light quantity distribution can beadjusted.

It is not necessary to deform the upper plate 7 and the lower plate 8symmetrically, and the plates 7 and 8 may be deformed independently aslong as the correcting amount of the light quantity distribution can beadjusted. When the plates 7 and 8 are deformed independently in such amanner, the correcting amount of the light quantity distribution can beadjusted more accurately.

As not shown, but also in the case of the grazing incidence, the platesare deformed and the installation position of the plates is shiftedsimilarly to the case of the front incidence, so that the correctingamount of the light quantity distribution may be adjusted.

This embodiment explains the aperture composed of a pair of the upperplate 7 and the lower plate 8, but an aperture composed of three or moreplates can be adopted.

According to the second embodiment, the aperture composed of a pluralityof the plates with the two-dimensional shape having the constant angleto the horizontal scanning direction is provided between the laser lightsource and the rotating polygon mirror. As a result, the light quantitydistribution on the sectional shape of the laser beam passing throughthe opening section formed by the combination of the plates can becorrected.

(C) Third Embodiment

A third embodiment explains a modified example of the diaphragm deviceaccording to the first and the second embodiments.

-   (C-1) The first embodiment explains the curved line shape of the    aperture last example. A flat plate having an opening section which    is provided vertically to the light advancing direction is adopted,    and the deforming adjustment units 20 (see FIG. 11) deform the shape    of the flat plate, so that the light quantity distribution may be    adjusted.

The shape of the opening section of the aperture is not particularlylimited, but it is desirably such that a height in the vertical scanningdirection on both ends or one end in the horizontal scanning directionis higher than a height in the vertical scanning direction on the centerportion.

The deforming adjustment units 20 move the installation position of theflat-plate aperture and/or changes the shape (for example, certaincurvature in the light advancing direction is given to the aperture andit is deflected). Since connection between the deforming adjustmentunits 20 and the aperture stabilizes the deforming operation of theaperture by mean of the deforming adjustment units 20, it is desirableto provide a fixed point (for example, a protrusion) for fixing theaperture in a position where the light flux of the incident light is notdisturbed.

Since the operation of the deforming adjustment units 20 is similar tothe operation explained in the first embodiment, its detail is omitted,but the operation can be adjusted according to conditions such as thefront incidence and the grazing incidence.

-   (C-2) In the first embodiment, the opening section has the    rectangular shape, but the opening shape can be such that the height    in the vertical scanning direction on both the ends or one end in    the horizontal scanning direction is higher than the height in the    vertical scanning direction on the center portion.

In this case, the opening shape is designed so that when the constantcurvature is given to the sectional shape of the aperture, the lightquantity distribution on a recording medium is uniformed. As a result,the light quantity distribution is adjusted only by the shape of thesectional curvature of the aperture in the first embodiment, but by theshape of the sectional curvature of the aperture and the opening shapeof the aperture in this embodiment. For this reason, the sectionalcurvature of the aperture can be reduced, and the installation space canbe reduced.

Further, the first embodiment can be applied only to the converged lightand diverged light, but this modified example can be applied also to theparallel light.

FIGS. 15A and 15B illustrate states that the light quantity of theparallel light is corrected. In FIG. 15A, the aperture of the firstembodiment, in which the height in the vertical scanning direction onboth the ends or one end of the opening shape in the horizontal scanningdirection is higher than the height in the vertical scanning directionon the center portion, is adopted. In FIG. 15B, the flat plate aperture,in which the height in the vertical scanning direction on both the endsor one end of the opening shape in the horizontal scanning direction ishigher than the height in the vertical scanning direction on the centerportion, is adopted. As shown in FIG. 15A, the opening shape is designedso that when a certain curvature is given, the light quantitydistribution is uniformed. As a result, when the curvature is increased,a quantity of the light passing through both the ends of the aperture isincreased, but when the curvature is decreased, the quantity of thelight passing through both the ends of the aperture can be reduced. Thatis to say, the light quantity can be adjusted to be increased ordecreased. On the contrary, the opening shape is designed so that thelight quantity distribution is uniform at the time of plane as shown inFIG. 15B. In this case, when the curvature is given in any directions,the light quantity is increased but cannot be decreased.

1. An optical beam scanning device, comprising: a light source; adeflection reflecting surface for deflecting to scan light from thelight source on a recording medium; and a diaphragm device providedbetween the light source and the deflection reflecting surface, thediaphragm device having an aperture formed by a nonplanar lightshielding section, the light shielding section making a light shieldingquantity of the light from the light source in a vertical scanningdirection different in positions of a horizontal scanning direction anda light advancing direction.
 2. The optical beam scanning deviceaccording to claim 1, wherein a sectional shape of the light shieldingsection in the horizontal scanning direction is a two-dimensional shape,a sectional shape of light flux passed through the aperture on the asurface of the two-dimensional light shielding section is such thatlight on a portion of the recording medium where a light quantity islarge is reduced and light on a portion where the light quantity issmall is increased.
 3. The optical beam scanning device according toclaim 1, wherein the diaphragm device includes a movable adjustmentsection for shifting an installation position of the light shieldingsection, deforming the light shielding section, and/or changing aninstallation angle of the light shielding section so that light quantitydistribution on the recording medium becomes uniform.
 4. The opticalbeam scanning device according to claim 2, wherein the diaphragm deviceincludes a movable adjustment section for shifting an installationposition of the light shielding section, deforming the light shieldingsection, and/or changing an installation angle of the light shieldingsection so that light quantity distribution on the recording mediumbecomes uniform.
 5. The optical beam scanning device according to claim1, wherein the light shielding section is composed of at least two ormore nonplanar light shielding plates which have a certain angle to thehorizontal scanning direction and are provided so as to shield the lightfrom the light source.
 6. The optical beam scanning device according toclaim 2, wherein the light shielding section is composed of at least twoor more nonplanar light shielding plates which have a certain angle tothe horizontal scanning direction and are provided so as to shield thelight from the light source.
 7. The optical beam scanning deviceaccording to claim 3, wherein the light shielding section is composed ofat least two or more nonplanar light shielding plates which have acertain angle to the horizontal scanning direction and are provided soas to shield the light from the light source.
 8. The optical beamscanning device according to claim 4, wherein the light shieldingsection is composed of at least two or more nonplanar light shieldingplates which have a certain angle to the horizontal scanning directionand are provided so as to shield the light from the light source.
 9. Theoptical beam scanning device according to claim 1, wherein a position ona stage before the diaphragm device and between the light source and thedeflection reflecting surface has a planar aperture plate in which anaperture on the plane has a shape such that a length in a directioncrossing a horizontal scanning direction on both ends or one end in ascanning direction is larger than a length on a center portion in thescanning direction.
 10. The optical beam scanning device according toclaim 2, wherein a position on a stage before the diaphragm device andbetween the light source and the deflection reflecting surface has aplanar aperture plate in which an aperture on the plane has a shape suchthat a length in a direction crossing a horizontal scanning direction onboth ends or one end in a scanning direction is larger than a length ona center portion in the scanning direction.
 11. The optical beamscanning device according to claim 3, wherein a position on a stagebefore the diaphragm device and between the light source and thedeflection reflecting surface has a planar aperture plate in which anaperture on the plane has a shape such that a length in a directioncrossing a horizontal scanning direction on both ends or one end in ascanning direction is larger than a length on a center portion in thescanning direction.
 12. The optical beam scanning device according toclaim 4, wherein a position on a stage before the diaphragm device andbetween the light source and the deflection reflecting surface has aplanar aperture plate in which an aperture on the plane has a shape suchthat a length in a direction crossing a horizontal scanning direction onboth ends or one end in a scanning direction is larger than a length ona center portion in the scanning direction.
 13. An optical beam scanningdevice, comprising: a cylindrical lens for condensing light from a lightsource; a deflection reflecting surface for deflecting to scan the lightfrom the light source on a recording medium; an aperture plate providedbetween the cylindrical lens and the deflection reflecting surface,aperture of the aperture plate on a surface having a shape such that alength in a direction crossing a horizontal scanning direction on bothends or one end in a scanning direction is larger than a length on acenter portion in the scanning direction; and a movable adjustmentsection for shifting an installation position of the aperture plateand/or giving certain curvature to the aperture plate and thus asectional shape of the aperture plate in the horizontal scanningdirection is a curved line shape so as to adjust light quantitydistribution on the recording medium uniformly.
 14. An optical beamscanning device, comprising: a light source; a deflection reflectingsurface for deflecting to scan light from the light source on arecording medium; an aperture plate provided between the light sourceand the deflection reflecting surface, an aperture of the aperture plateon a surface having a shape such that a length in a direction crossing ahorizontal scanning direction on both ends or one end in a scanningdirection is larger than a length on a center portion in the/scanningdirection, sectional shape of the aperture plate in the horizontalscanning direction being a two-dimensional shape; and a movableadjustment section for moving an installation position of the apertureplate and/or giving certain curvature to the aperture plate so that thesectional shape of the aperture plate in the horizontal scanningdirection is a curved line shape so as to adjust light quantitydistribution on the recording medium uniformly.
 15. A diaphragm devicecomprising: an aperture on a surface of a nonplanar light shieldingsection, wherein the light shielding section shields light so that aposition where incident light of converged/diverged light or parallellight is shielded is differed with a light advancing direction accordingto positions in alight section.
 16. A diaphragm device comprising: anaperture on a surface of a nonplanar light shielding section, whereinthe light shielding section determines a quantity of incident light ofconverged/diverged light or parallel light to be shielded according topositions in a light section and positions of a light advancingdirection.
 17. The diaphragm device according to claim 15, furthercomprising: a movable adjustment section for moving an installationposition of the light shielding section and/or deforming the lightshielding section, wherein light quantity distribution is adjusted on asurface in a predetermined position to which light passing through theaperture is emitted by shift or deformation of the light shieldingsection using the movable adjustment section.
 18. The diaphragm deviceaccording to claim 16, further comprising: a movable adjustment sectionfor moving an installation position of the light shielding sectionand/or deforming the light shielding section, wherein light quantitydistribution is adjusted on a surface in a predetermined position towhich light passing through the aperture is emitted by shift ordeformation of the light shielding section using the movable adjustmentsection.